Mastocytosis can lead to organ failure as well as systemic symptoms that can be disabling, with considerable deterioration in quality of life. Beside symptomatic treatments, interferon-α and purine analogues have been shown to be effective but complete or long-term remission is rarely obtained with these drugs. We conducted a phase II, multicentre, study to investigate thalidomide in severely symptomatic indolent and aggressive systemic mastocytosis. Twenty patients were enrolled of whom 16 were analysed for response. The overall response rate was 56%. Responses were observed in the skin in 61% of patients with a significant decrease in the pruritus score. Mast cell mediator-related symptoms responded in 71% of cases and 25% of aggressive systemic mastocytosis patients had a response in terms of B/C findings (borderline/cytoreduction needed). Bone marrow mast cell infiltration decreased in five of the eight evaluable patients. There was no significant improvement in the AFIRMM (Association Française pour les Initiatives de Recherche sur le Mastocyte et Les Mastocytoses), Quality of Life or Hamilton scores. Grade 3-4 toxicities consisted of peripheral neuropathy (11%) and myelosuppression (neutropenia: 5%; thrombocytopenia: 11%). In conclusion, thalidomide might be useful in mastocytosis and in the treatment of mast cell-related symptoms. It might be considered in selected patients, taking into account the benefit/risk balance and the individual patient evaluation.
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